Polymer foams are commonly made by using a blowing agent with molten resin under pressure and, after thorough mixing, extruding the combination through an appropriate die into a lower pressure atmosphere.
In the past, physical blowing agents widely used for making foams were chlorofluorocarbons and hydrochlorofluorocarbons. Use of such blowing agents, however, will likely be banned because of their high ozone depletion potential (ODP). Some of these blowing agents can be replaced with hydrofluorocarbons (HFCs), which have zero ODP. However, HFCs are associated with high global warming potential (GWP).
Presently, physical blowing agents more commonly used for making thermoplastic polymer foams such as alkenyl aromatic polymer (e.g, polystyrene) or polyolefin polymer (e.g. polyethylene) foams, are butanes and isopentane. Hydrocarbons with three or more carbons atoms, however, are considered volatile organic compounds (VOCs) that lead to the formation of smog. Furthermore, some compounds currently used in blowing agent compositions are hazardous air pollutants (HAPs). The use of VOCs and/or HAPs for preparing polymeric foams is not preferred environmentally and imposes many limitations on the manufacturing process, thus complicating and significantly increasing the cost of manufacturing. Ethane is classified as a non-VOC because of its very low photochemical reactivity. The photochemical reactivity of methyl formate is even lower than that of ethane and, therefore, it can be considered to have negligible propensity to form smog. Furthermore, methyl formate is classified as a non-HAP, has zero ODP, and an almost zero GWP. Thus, a blend of methyl formate with some of the blowing agents in current use can help offset the harmful environmental impacts (ODP, GWP, HAP, VOC) associated with the blowing agents in current use. U.S. Pat. No. 6,753,357 describes the use of methyl formate to produce stable, rigid isocyanate/polyol based polyurethane foams. Such foams are thermoset foams made via a cross-linking and curing process, and the dimensional stability or instability imparted to the final foam product by the nature of the blowing agent is quite different than in the case of the melt processed thermoplastic polymer foams. Therefore, a need exists for blowing agents employing methyl formate as the sole or one of the components of the blowing agent blend to produce stable thermoplastic foams without compromising the product quality in terms of appearance, mechanical or compressive strength and insulation value, and that enable a cost-effective and versatile manufacturing process.